docs: def change_radius(self, selections, value):
          '''Change the radius of each atom by a certain value
          
          '''
          if 'atoms' in selections:
              atms = selections['atoms'].mask
              if value is None:
                  self.radii_state.array[atms] = [vdw_radii.get(t) * 0.3  for t in self.system.type_array[atms]]
              else:
                  self.radii_state.array[atms] = value
      
          self.update_scale_factors(self.scale_factors)